Operators use packers downhole to isolate portions of a wellbore's annulus when performing various operations. For example, operators can selectively frac multiple isolated zones by deploying a tool string having one or more packers into an open or cased wellbore. When activated, the packers isolate the wellbore's annulus so the isolated zones can be separately treated.
Different types of packers can be used in the wellbore. One conventional packer uses a compression-set element that expands radially outward to the borehole wall when subjected to compression. Being compression-set, the element's length is limited by practical limitations because a longer compression-set element would experience undesirable buckling and collapsing during use. However, a shorter compression-set element may not adequately seal against irregularities of the surrounding borehole wall. Moreover, this type of packer typically needs a sophisticated mechanism to actuate the compression-set element.
Another conventional packer uses an inflatable element. When deployed, a differential pressure is introduced to inflate the element so that it produces a seal with the surrounding borehole wall. Compared to a compression-set packer, however, the inflatable packer can be significantly more costly and can be more difficult to implement and deploy.
Another conventional packer uses a swellable element. When run into position downhole, fluid enlarges the swellable element until it produces a seal with the borehole wall. This can take up to several days to complete in some implementations. Once swollen, the element's material can begin to degrade during its continued exposure to the fluid, and a high differential pressure or an absence of the activating fluid that swelled the element can compromise the swellable element's seal.
In addition, the swellable element may become extruded if it is allowed to swell in an uncontrolled manner. To limit the axial swelling of the element, metal rings can anchor the top and bottom of the swellable element and prevent it from expanding axially beyond the anchoring points. Examples of such metal rings are used by TAM International and Swelltec. Backup rings may also be used in addition to the metal anchoring rings at either end, as done by Easywell, for example.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.